1. Field of the Invention
The present invention relates generally to a shutter construction and, more particularly, to a camera shutter and a driving device in which a piezoelectric element is employed for opening and closing shutter blades of the camera shutter.
2. Related Art
There are various types of camera shutters, most of which are adopted to use a spring and/or a motor as a drive source for opening/closing shutter blades of the camera shutter. A conventional shutter construction using a step motor as the drive source for opening/closing the shutter blades is disclosed, for example, in Examined Published Japanese Utility Model Publication No. 62-142035 or in Examined Published Japanese Patent Application No. 4-74693.
As an example of the construction adopting the step motor as the drive source for opening/closing the shutter blades, a motor driven shutter as disclosed in the Examined Published Japanese Utility Model No. 62-142035 will be described below. The step motor is constructed by winding coils on a pair of stators attached to a base plate and by fitting a rotor having a permanent magnet in a space, which is surrounded by the magnetic pole portions of the individual stators, such that the rotor shaft is disposed vertical to the stators. A rotor pinion is fixed on the rotor shaft so that the shutter blades are rocked by the rotation of the rotor through a gear train including the rotor pinion.
In the conventional motor driven shutter described above, the mechanism for driving the shutter blades has a complex construction because it requires a motor comprising stators, coils and a rotor, and a gear train for transmitting the rotation of the motor to the shutter blades. Although the drive mechanism disclosed in Examined Published Japanese Utility Model No. 62-142035 is designed to suppress an increase in size of the mechanism as much as possible, a reduction of the overall size of the shutter is still restricted due to the requirement of a motor for opening/closing the shutter blades as described above. For example, in order to increase the opening/closing rate of the shutter blades (i.e., the shutter speed), a higher motor rotation speed is required. In order to increase the speed of the motor, however, an increase in the number of coil turns is required. Accordingly, the overall construction of the camera shutter becomes complicated and a meaningful reduction in size (e.g., thickness) of the camera shutter is not rendered possible.